AT&T on Wednesday reported impressive first-quarter iPhone activations that hardly seemed affected by the carrier’s recent loss of iPhone exclusivity. Now, investment research firm ITG is suggesting Verizon Wireless’ iPhone 4 might not even be the carrier’s top seller anymore. As reported by the New York Post, ITG claims that the 4G LTE-capable HTC ThunderBolt overtook the iPhone last month to become Verizon’s No. 1 smartphone. The Post did not report March sales figures for the ThunderBolt or the iPhone, though it did say Verizon had only sold a total of 2 million iPhone 4 units through the end of March. Apple is scheduled to report its second-quarter earnings on Wednesday, and analysts are expecting iPhone sales to total 16-17 million units.